1. Field of Invention
The present invention relates to a rechargeable battery structure and the method of making the same and, in particular, to a rechargeable battery structure adopting S-shape folding on the electrolytic cells and the method of making the same.
2. Related Art
Recent developments in rechargeable secondary power storage devices, such as the lithium-ion secondary battery, the high efficiency nickel hydrogen battery, and the super capacitor, are becoming mature; there are good performances in energy density, power density and battery lifetime. As electronic elements get miniaturized, the weight and volume of the battery is also forced to minimize. However, in this miniaturizing process, the energy capacity and lifetime of the battery are only allowed to increase but not to decrease. Furthermore, the safety concern is still the primary consideration. Thus, there is still need for a new movable energy source.
Usual batteries can be classified into two types: the cylindrical type and the rectangular type. The 3C battery module uses mostly the rectangular type batteries because they are more effective in space. Conventional rectangular battery cell elements are rolled into a spiral coil, resulting in certain die volume (usually on the four corners) in the battery. This die volume is filled with electrolyte; so it causes the loss in energy density and lowers the cycle lifetime of the battery. More seriously, there are safety concerns about possible electrolyte leakage.
In view of the foregoing, it is an object of the present invention to provide a new rechargeable battery structure, which is a stacked structure of sequentially folded cells that can increase the energy density while decreasing die volume of the battery.
The rechargeable battery structure according to the above object of the invention comprises a plurality of flexible electrolytic electrode layers and interposed electrolytic material arranged by sequential folding. wherein the positive and negative electrodes comprise a current collector coated with cathode and anode active materials, respectively. The structure is characterized in that (a) the electrolytic cell layer is a stacked cell structure formed by S-shape folding; and (b) the cathode and anode active materials are coated at intervals on the current collector by interposition and no cathode and anode active materials are coated at folded places.
Furthermore, the present invention provides a method of making the rechargeable battery of the above-mentioned stacked structure.
Pursuant to the above object, the method of making the rechargeable battery comprises the steps of: (a) providing a flexible electrolytic cell layer, which comprises a plurality of pairs of positive and negative electrodes for chemical reactions and interposed electrolytic material, and the positive and negative electrodes including cathode and anode active materials coated at intervals on two current collectors, respectively; (b) folding the electrolytic cell layer at the places where no cathode and anode active materials are coated so as to get a stacked cell structure of electrolytic cells stacked successively; (c) squeezing the stacked cell structure by pressure and putting it into a battery case; and (d) filling electrolyte and encapsulating.
Since this new battery structure takes the sequential S-shape folding, the gas pressure generated around the electrodes due to improper operation, such as charging or short-circuiting, would not accumulate in concentric circles but expand toward both ends of the electrodes. Therefore, this structure design of the electrodes satisfies the safety requirement. Furthermore, since folding is employed, the volume usage rate is greatly increased. No excess electrolyte is supplied due to too much die volume. Therefore, in addition to the increase in the energy density and the charge/discharge cycle lifetime, this structure also significantly eases the safety worry about too much electrolyte. In the aspect of the battery thickness, the lithium ion rectangular battery utilizes a blade or a diamond tool to spiral the cell to obtain a thinner battery structure. Although 3 mm can be reached in principle, the current ones have a thickness of about 4.5 mm to 8 mm. The new design of the battery structure can have a thickness below 2 mm done without using any tool.
Since the battery structure of the invention takes the rectangular shape, it has a superior heat ventilation mechanism. Therefore, the invention is suitable for applications requiring large batteries such as the electric vehicle. This structure can then replace large cylindrical vehicle batteries currently used.
Current lithium ion secondary batteries comprises organic electrolyte in conjunction with the anode material, such as LiCoO2, LiMn2O4, LiNiO2, or LiCoxc3x97Ni(1xe2x88x92xc3x97)O2, where x is a fractional number between 0 and 1, and the cathode material, such as graphite, carbon, MCMB, and lithium. Also, a separator membrane must be provided between positive and negative electrodes to prevent short-circuiting. The organic electrolyte is permeated between porous plasticized separator membranes for ionic conduction. Since the electrolyte is a liquid, a metal case has to be employed for the sake of safety. The drawback is that metal cases can not be fabricated too thin. Moreover, the aluminum foils used in polymeric batteries are cheaper in cost. Therefore, the lithium ion battery with the new battery structure of the invention must be superior in both thickness and cost.
For the most part, the sequential folding structure disclosed in the present invention can provide features such as a higher safety, higher energy density, higher cycle lifetime and good conductivity at a high temperature.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.